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Antihydrogen Abounds

Antihydrogen has it all backward, yet the topsy-turvy antimatter substance still obeys the rule that more is better. Just a few weeks after one team of antihydrogen-making physicists announced that it had created 50,000 atoms of cold antihydrogen, a rival team says that it has created more than three times as many and is starting to analyze their properties.

Ordinary hydrogen is made of a light, negatively charged electron orbiting a heavy, positively charged proton. Antihydrogen is exactly the opposite: A light, positively charged antielectron orbiting a heavy, negatively charged antiproton. Because antielectrons and antiprotons are hard to come by and are usually moving very fast when they are created, it's a tough job to slow them down enough to form antihydrogen atoms. By studying whether antihydrogen behaves differently from hydrogen, physicists hope to learn a great deal about the fundamental relations between matter and antimatter.

But to study antihydrogen, you have to make it and detect it. Last month, the ATHENA team at CERN announced that it had cooled antiprotons and antielectrons in a magnetic bottle and detected gamma rays that stream from the annihilation of the antihydrogen when it collides with a chunk of matter (ScienceNOW, 18 September).

Now Gerald Gabrielse, a physicist at Harvard University, has announced that his ATRAP team, also based at CERN, has created antihydrogen using a similar magnetic bottle. Their instrument has one extra feature: It allows neutral particles such as antihydrogen to flow into an ionization well, a trap that pulls apart the antihydrogen. By counting the antiprotons that are torn away from their antielectrons, the team got an unambiguous sign that ATRAP had created antihydrogen, and by analyzing how strong a field must be before it tears apart an antihydrogen, physicists can tell how tightly bound the antielectron is to the antiproton. "What we could tell is that they're in a very loosely bound state," says Gabrielse. "It's really exciting to get a first glimpse into the [anti]atom."

"I personally believe it. It's a very interesting result and very exciting," says Rolf Landua, a physicist at CERN with the ATHENA collaboration. But the real goal of both collaborations is to trap enough slow-moving antihydrogen so researchers can zap it with a laser and see what light it absorbs and emits--an atom's "fingerprint." Neither ATRAP nor ATHENA can do this yet, but with both teams announcing their first significant results, the game is certainly afoot.